This invention relates generally to vibratory compactors, and more particularly to the usage of a linear actuator to vibrate the surface contacting member of a vibratory compactor.
Vibratory compactors typically comprise a plate or roller that is oscillated or vibrated to impose compaction forces on a densifiable strata, such as ground soil, roadway base material, or paving material. In most instances, an engine or hydraulic motor controllably rotates at least one eccentric mass to impart vibratory motion at a particular frequency to the surface contacting plate or roller member. The result is an oscillatory force with the frequency of the speed of rotation, and an amplitude dependent on the mass eccentricity and speed of rotation. Variations on this basic system include multiple eccentric weights and/or shafts such that by changing the phasing of the multiple weights and/or shafts, the degree of force created by the eccentric masses can be varied. For instance, U.S. Pat. No. 3,909,147 to Takata teaches a variable amplitude vibration generator for a compactor.
Although these systems have proven effective, there remains room for improvement. Current rotating eccentric mass systems often have a limited range of available frequencies and amplitudes, and more often this range is limited to a few discrete frequencies. More recently, engineers have observed that, depending upon the particular conditions, the compaction process can be substantially improved and/or hastened by having the ability to adjust the vibration frequency and/or amplitude to suit the particular conditions. U.S. Pat. No. 5,942,679 to Sandstrom discusses some of these issues.
In addition, paving compaction machines are now facing new challenges due to the introduction of so called xe2x80x9csuperpaversxe2x80x9d. These new paving compounds often require a higher rate of compaction because they must be compacted within a narrow compound temperature range. This can dictate the requirement that the compactor either be more efficient in compacting the strata and/or have the ability to effectively compact while moving faster. In addition, these new superpavers can sometimes have aggregates that make them harder to compact. In order to meet these demands, a next generation of vibrating compactors needs to operate more efficiently and be equipped to provide a larger variety of vibration frequencies and amplitudes. These improvements need to be accompanied by improved reliability at a competitive cost.
One alternative method of generating vibrations without reliance upon a rotating eccentric mass is disclosed in U.S. Pat. No. 6,293,729 to Greppmair. That reference teaches a walk behind compactor for compacting soil that includes an internal combustion engine that is coupled to drive a working mass linearly up and down via a crank mechanism and spring assembly. This reference also teaches the idea of reciprocating a counter mass out of phase with the working mass, presumably to reduce the amount of vibration transferred to the user via the compactor framework. Although the Greppmair compactor diverges from earlier compactors in its use of a linearly displaced working mass, it retains many of the drawbacks associated with earlier vibratory compactor strategies that rely upon a rotating shaft driven by an engine or other motor to supply the motion and energy for producing the compacting vibration.
The present invention is directed to one or more of the problems set forth above.
In one aspect, a compactor includes a surface contacting member attached to a chassis. A linear oscillator is operably coupled to vibrate the surface contacting member. The linear oscillator includes at least one electromagnetic force generator.
In another aspect, a compactor includes a first roller and a second roller that are rotatably attached to a chassis. A first linear oscillator is operably coupled to vibrate the first roller, and a second linear oscillator is operably coupled to vibrate the second roller.
In still another aspect, a method of compacting a stratum includes a step of vibrating a surface contact member of a compactor. The vibrating step includes a step of actuating a linear oscillator operably coupled to vibrate the surface contacting member. The actuating step includes a step of energizing at least one electromagnet.